By making your type readable, you immediately jump ahead of at least half of the competition, which is fortunate, really, because it's not that hard!
As a general rule, designers like to set their body copy at the very least at 12px. Most, however, chose a larger size like 14px, which is even better for readability. Font-sizing is really quite easy to decide on for body copy, but it's the titles that start to get complicated.
. Generally speaking, for large blocks of text, 1.5 times the size of the text is a good size.